"We shall not boycott. I repeat, we shall not boycott and we will participate fully in the National Assembly elections and the presidential elections," said All Nigeria People's Party chairman Edwin Ume-Ezeoke, who is also Mr Buhari's running mate.

"The party has decided that as true and patriotic democrats, we do not want to unconsciously become tools in the hands of the PDP-led government in their tenure elongation programme."

Mr Abubakar agreed with these sentiments.

"You have to participate to challenge the wrongdoings in the courts," he told the BBC's Focus on Africa programme.

He said it would be better to field a common opposition candidate, but Mr Buhari disagreed that the failure to do so would hand over victory to the PDP.

"It hasn't handed it over. If that is your assumption, it is the wrong assumption," he told the BBC.

Mr Abubakar's participation in the poll was only confirmed on Tuesday by the election commission, after a Supreme Court ruling on Monday.

The Independent National Election Commission (Inec) had disqualified him because of charges of corruption, which he denies.

Many Nigerians fear further violence on Saturday, which should lead to the first handover of power in Africa's most populous nation from one civilian administration to another.

Meanwhile, in the northern city of Kano, the military says it is continuing to clear a group of Islamic militants away from the Panshekara district on the outskirts of the city after two days of clashes, which have left at least 38 people dead.